Water games by mountain gorillas: implications for behavioral development and flexibility-a case report

Chimpanzee play sequences are structured hierarchically as games

Social play is ubiquitous in the development of many animal species and involves players adapting actions flexibly to their own previous actions and partner responses. Play differs from other behavioural contexts for which fine-scale analyses of action sequences are available, such as tool use and communication, in that its form is not defined by its function, making it potentially more unpredictable. In humans, play is often organised in games, where players know context-appropriate actions but string them together unpredictably. Here, we use the sequential nature of play elements to explore whether play elements in chimpanzees are structured hierarchically and follow predictable game-like patterns. Based on 5,711 play elements from 143 bouts, we extracted individual-level play sequences of 11 Western chimpanzees (Pan troglodytes verus) of different ages from the Bossou community. We detected transition probabilities between play elements that exceeded expected levels and show that play elements form hierarchically clustered and interchangeable groups, indicative of at least six games that can be identified from transition networks, some with different roles for different players. We also show that increased information about preceding play elements improved predictability of subsequent elements, further indicating that play elements are not strung together randomly but that flexible action rules underlie their usage. Thus, chimpanzee play is hierarchically structured in short games which limit acceptable play elements and allow players to predict and adapt to partners' actions. This "grammar of action" approach to social interactions can be valuable in understanding cognitive and communicative abilities within and across species.

Swimming and diving as social play in juvenile rhesus macaques (Macaca mulatta)

Although play is ubiquitous throughout the animal kingdom, and in primates especially, the ultimate explanations and proximate mechanisms of play are not well understood. Previous research proposes that primate play may be important for the development of cognitive skills including executive function, emotional regulation, and impulse control, and could help to build social skills and network connections needed in later life. However, many of these hypotheses have not been thoroughly tested. Here, we report observations of novel play behaviour that could provide unique opportunities to explore these hypotheses: young rhesus macaques (Macaca mulatta) engaging in aquatic social play in a naturalistic setting. Based on our observations, we propose that aquatic play has social elements that make it ideal for testing ultimate explanations of primate play and hypotheses about the cognitive mechanisms that support it.